On-board aircraft transducer

ABSTRACT

WEIGHT SUPPORTED BY A WHEELED VEHICLE SUCH AS AN AIRCRAFT IS DETECTED INSIDE HOLLOW AXLES BY STRAIN-GAGE TRANSDUCERS WHICH ARE LOCKED IN PLACE BY INDIVIDUALLY ADUSTABLE SPRINGING-TYPE COLLETS MAKING SUBSTANTIALLY LINE-CONTACT CONNECTIONS WITH INTERIOR AXLE SURFACES, THE COLLETS FOR EACH TRANSDUCER ARE CARRIED BY RIGID END PORTIONS OF A SENSING SECTION INCLUDING AT LEAST ONE DEFORMABLE TUBULAR PORTION EQUIPPED INTERNALLY WITH STRAIN GAGES ARRANGED TO CHARACTERIZE SHEAR EFFECTS CAUSED BY THE WEIGHT, AND, IN APPROPRIATE CASES WHERE INSTALLED WITHIN AXLES HAVING NONUNIFORM THICKNESS, THE SENSING SECTION IS OF AN ASYMMETRICAL CONSTRUCTION INTRODUCING SELF-COMPENSATION FOR MEASUREMENT ERRORS INDUCED BY AXLE NON-UNIFORMITY.

Dec. 7, 1971 E. LAIMINS 3,625,053

ON-BOARD AIRCRAFT TRANSDUCER Filed Jan. 14, 1970 4 Sheets-Shoot 1INVENTOR EFC LAIMINS ATTOR N I'IY Dec. 7, 1971 E. LAIMINS 3,625,053

ON-BOARD AIRCRAFT TRANSDUCER Filed Jan. 14, 1970 4 Sheets-Sheet 2 45%G39 v 552 H615 42 mvnu'ron ERIC LAIMINS gum/aw ATTORNEY Dec. 7, 1971 E.LAIMINS ON-BOARD AIRCRAFT TRANSDUCER 4 Sheets-Sheet Filed Jan. 14, 1970mvsmon ERIC LAIMINS BY M 5 W ATTORNEY DH:- 7, 1971 L N5 3,625,053

ON-BOARD AIRCRAFT TRANSDUCER Filed Jan. 14, 1970 4 Sheets-Sheet 4.

FIG. .9

mvmwon EPIC LAIMlNS United States Patent 3,625,053 ON-BOARD AIRCRAFTTRANSDUCER Eric Laimins, Belmont, Mass., assignor to BLH Electronics,Inc., Waltham, Mass. Filed Jan. 14, 1970, Ser. No. 2,892 Int. Cl. G0117/16, /12

US. Cl. 7388.5 19 Claims ABSTRACT OF THE DISCLOSURE Weight supported bya Wheeled vehicle such as an aircraft is detected inside hollow axles bystrain-gage transducers which are locked in place by individuallyadjustable spring-type collets making substantially line-contactconnections with interior axle surfaces; the collets for each transducerare carried by rigid end portions of a sensing section including atleast one deformable tubular portion equipped internally with straingages arranged to characterize shear effects caused by the weight; and,in appropriate cases where installed within axles having nonuniformthickness, the sensing section is of an asymmetrical constructionintroducing self-compensation for measurement errors induced by axlenon-uniformity.

BACKGROUND OF THE INVENTION The present invention relates toimprovements in the measurement of loadings such as those which areeffective at the wheels of aircraft and the like, and, in one particularaspect, to novel and improved on-board aircraft weighing transducerswhich cooperate with axle structures of even non-uniform thickness todevelop strain gage outputs characterizing weight-related verticalforces, and which incorporate unique readily-adjustable and highlysecuremounting provisions.

As has long been well known, measurements of aircraft weights atdistributed sites such as those of the usual landing gear provide datafrom which total weight and locus of the center of gravity may readilybe calculated as important aids to safe and efficient aircraftoperation. Although accessory weighing jacks and platform-type scalesare capable of determining these weights accurately, it offers obviousadvantage to integrate the weighing instrumentalities on-board wherethey may be used at any ground location at any time without involvingoutside equipment and personnel. Accordingly, for the latter purposes,it has been proposed that the sensing techniques might include mountingotentiometer-type detectors or strain gages directly on the wheel strutsor in association with deformable members responsive to pressures in thehydraulic wheel suspensions. As a practical matter, such techniques arefound to be wanting in that have not succeeded in avoiding seriouserrors due to responses to forces other than those representingmerelythe craft weight; in hydraulic or pneumatic systems, for example, thereare highly disturbing effects of friction between relatively movableparts, and in the strut-gaging systems the measurements unavoidablyreflect unwanted responses to side loadings due to such factors as wind,apron discontinuities or slopes, and uneven tire wears or inflations.The allowable margin of error in calculations of aircraft center ofgravity is very small, because of the great hazards which can resultfrom faulty information as to its whereabouts in what invariably a verylimited permissable range to begin with on any craft.

In accordance with certain aspects of the recognitions and teachings ofthe invention of US Pat. No. 3,426,586, assigned to the same assignee asthat of the present application, on-board transducers of a strain-gagetype may be caused to respond with extraordinary precision to load-3,625,053 Patented Dec. 7, 1971 ing forces which produce shear in wheelaxles of aircraft landing gear, with the result that their responsesaccurately characterize true weight reactions which are essentiallyisolated from the usual error-inducing effects differently evidencingthemselves as bending. Isolation of shear is promoted by mounting agaged shear-responsive element upon a wheel axle by way of spaced fittedcollets which are in line contact with the axle, and the outputs arepreferably improved through use of a sensing section including at leastone deformable tubular portion equipped internally with strain gagesintended to characterize only shear effects caused by the weight.However, it has been found that prior colleting has been difficult toinstall and adjust into secure locked positions, particularly within theconfines of hollow axles which are expected to withstand extremes ofshock, vibration, temperature, contamination and like environmentalconditions. Moreover, the sensing portions of such transducers must becarefully and precisely oriented or zeroed within the axles, and priormulti-part adjustment provisions do not offer the ease and security ofadjustments which would be optimum in many installations. In addition,transducers which suffice for measurements within axles exhibitinguniform cross-sections along the regions of the transducers, are foundto be subject to errors, mainly due to unwanted responses to bendingrather than shear effects, when the axles are non-uniform or areeffectively non-uniform because of influences of other members. Thepresent teachings enable difficulties of the aforesaid character to beovercome, by way of transducer structure of low-cost manufacture whichis exceedingly rugged, easily installed and adjusted, readily adaptableto uses with non-uniform axles, and, further, is tunable to improveprecision of measurements by offsetting unwanted bending responses.

SUMMARY OF THE INVENTION It is one of the objects of the presentinvention, therefore, to provide novel and improved transducer apparatusof low-cost rugged construction which is uniquely adjustable to provideaccurate measurements of vehicle loadings in response to axledeflections.

Another object is to provide new and advantageous strain-gagetransducers having improved collet mounts capable of supporting asensing section securely within a hollow axle under extremeenvironmental conditions of use, and which are nevertheless readilyinstalled and finely adjustable in situs.

An additional object is to provide shear-responsive strain-gagetransducers which may be installed in-init'ial stress-free or zeroedrelationship within hollow vehicle axles, and which are uniquelyproportioned for precise measurement of wheel reactions in verticaldirections independently of side loadings and related bendingmomenteffects, even with axles of non-uniform crosssection.

:Further, it is an object to provide unique onboard aircraft weighttransducers of essentially one-piece construction which may be quicklyand reliably mounted and precisely adjusted within tubular wheel axlesby Way of individually-expansible portions of line-contacting colletmembers, and which involve shear-responsive strain-gage sensors whichadvantageously promote maximum outputs and effect cancellations ofunwanted bending-moment reactions which would otherwise result from axlenon-uniformities.

A still further object of the present invention is to provide animproved onboard aircraft weight transducer having tubularshear-responsive sensing sections which involve deformable portionsseparated by a more rigid portion to promote optimum outputs, and whichare suPP rted asymmetrically to promote suppression of unwantedbending-moment effects not related to the weight under measurement.

By way of a summary account of practice of this invention in one of itsaspects, the weight supported by each wheel of an aircraft is detectedby a strain-gage transducer mounted within the usual hollow axleassociated therewith, the sensing section for the transducer includingat least one relatively flexible tubular portion asymmetrically disposedto a predetermined degree in relation to mounts for relatively rigid endportions united therewith, such that unwanted bending effects do notproduce erroneous outputs from the circuitry of strain gages housedwithin the sensing section. Each of the rigid end portions of thesensing section is supported by a pair of diametrically-opposedradially-expansible collet members, and each of the collet members is ofa bowed form rendering it individually adjustable, radially, by way ofaxial compression via an adjusting member. The said collet members areradially expansible to make secure and essentially line-contactconnections with the interior of the axle, and to provide stable andrigid internal suspensions for the rigid ends of the sensing section.Further, they act as somewhat resilient supports which will compensatefor internal dimensional changes in the axle due to environmentaleifects, and, because of the individual radial adjustabilities, thecollet members provide an important convenient means for eliminating oradjusting the orientation of and pre-load forces experienced by thesensing section when it is first installed. Strain gages bonded to thetubular members at diametrically-opposite positions respond to bothbending and shear effects, but due to the combined effects of properlylocating the gages and mechanically adjusting the unique collets,unwanted responses due to bending effects are eliminated and the outputsare related substantially to shear alone. The latter outputs are, inturn, accurately related to the wheel reactions due to craft weight,without including error-inducing components resulting from sideloadings, and with minimized shifts due to exposures to environmentalextremes.

BRIEF DESCRIPTION OF THE DRAWINGS Although the aspects and features ofthis invention which are believed to be novel are expressed in theappended claims, additional details as to preferred practices andembodiments, and as to the further advantages, objects and featuresthereof, may be most readily comprehended through reference to thefollowing description taken in connection with the accompanyingdrawings, wherein:

FIG. 1 illustrates an aircraft landing gear assembly in which dashedlinework characterizes bending and shear deflections, together withrelated bending moment and shear diagrams;

FIG. 2 is a cross-section of an improved axle-mounted shear transducerin a neutral or undeflected condition, and without radial adjustments;

FIG. 3 is a cross-section taken along section line 3-3 in FIG. 2;

FIG. 4 represents'an inner cylindrical surface of the transducer ofFIGS. 2 and 3 together with strain gages carried thereon;

FIG. 5 schematically illustrates bridge circuit connections for gagessuch as those of FIG. 4;

:FIG. 6 provides a cross-section of the same axlernounted transducer ina condition of substantially pure shear;

FIG. 7 provides a cross-section of the same transducer undergoingbending;

FIG. 8 is a pictorial illustration of a preferred embodiment of animproved transducer, without radial adjustment members;

FIG. 9 comprises a longitudinal cross-section of the transducer of FIG.8 together with a surrounding axle of non-uniform cross-section in axialdirections;

FIG. 10 is a view of the transducer in FIG. 9, taken along section line10--10 in FIG. 9;

FIG. 11 is a view, partly in section, of another collet arrangement;and,

FIG. 12 comprises a partly pictorial and schematic diagram of anon-board weight-responsive system into which the improved transducersmay be incorporated.

DESCRIPTION OF THE PREFERRED EMBODIMENT The paired aircraft wheels 19and 20 appearing in FIG. 1 represent part of a landing gear unit whichbears some of the loading typically shared by a plurality of units in alanding gear array. Conventional tubular forms of an axle 21 and strut22 communicate downward force 23 of the ground-supported aircraft to thewheels and thence to the underlying apron surfaces. Wheel reactions tothe vertical loading are characterized by force arrows 24 and 25, andnormally are about equal. In addition to the downwardly-directed forcesrepresenting the aircraft weight which is of interest for measurementpurposes, the wheel-reactions can be expected to involve lateralcomponents, such as are designated by arrows 26 and 27, as theunavoidable result of such factors as wind loading, apron slope orirregularities, parking stresses, uneven tire inflations or wear, andthe like. Resulting deflections of the halves of axle 21 reflect theeifects of both bending moment and shear; bending moments tend to causethe kind of deflections designated by dashed linework 28, and sheardeflections tend to be of the nature designated by dashed linework 29.Bending moment varies with position along the longitudinal axis of axle21, of course, and represents the vertical load multiplied by thedistance between that position and the center of pressure of the tire onthe underlying apron, plus any lateral loads multiplied by the tireradius. As has already been referred to, the side loads may vary and theradius and center of pressure, or footprint, of the tire may changealso. Bending moment plot 30 shows variations with distance, consideringonly the vertical load reactions 24 and 25 while they remain constant,and plots 31 and 32, characterize the net bending moments due to thecombined eifects of these vertical load reactions with the horizontalside loads 26 and 27, respectively. When transducers responsive tobending moments are employed, their axial positions are thus critical,and moreover, the contributions due to side loadings cannot besegregated and the measurement can be seriously in error if they aretaken to represent craft weight. By way of important distinction,however, the shear plot 33 characterizes only the forces in the verticaldirection, as desired, and is even essentially independent of thepositions along each half of the axle.

Based upon recognitions of the latter advantages, a shear-responsivetransducer 34 (FIG. 2) is disposed within each half of the hollowcylindrical axle 21 to sense and characterize only the shear effectswhich take place due to weight-related forces acting in the verticaldirection. The sensing element includes spaced rigid end portions 35aand 35b and an intermediate sensing section including spaced relativelythin-walled flexible tubular portions 350 and 35d, the rigid endportions each being separately suspended within the axle bydiametrically opposed radially expansible collects 35a, 35b, 37a and37b, which are seen to be doubly-bowed and can be individuallycompressed laterally to cause firm substantially line-contactengagements with the inner axle surface 21a as the result of toggle-likeradial expansion of the collets. Electrical shear-responsive straingages are bonded to interior surfaces (such as 35c in FIG. 4) of therelatively thin flexible portions 350 and 35d at each of two oppositeupper and lower positions along a vertical diameter at the respectiveportions, where they also will unavoidably respond to certain tensionand compression effects exhibited at these sites due to unwantedbending, such as that caused by side loadings mentioned above. Furtherimportant advantages result from the fact that this unique form of shearsensor well lends itself to construction as a small light-weight elementwhich does not add significantly to the craft loading, which may beflexible and sensitive enough to develop large responses, and which maybe machined simply and accurately. Collaterally, it is important thatthe preferred colleting, described in detail later herein, need not beadjusted in a manner which would tend to impose forces disturbing thelightweight construction of the sensing element. In FIG. 4, wherein thecylindrical inner sensor surface 350' is opened out flat for purposes ofillustration, the top strain gage 39, is shown to have its wire grid 39aaligned substantially parallel with the longitudinal axis of the sensor,and the bottom strain gage 40 has a like wire grid 40a, with itsfilaments similarly aligned. The cornpanion gages 41 and 42 at the topand bottom of the interior of sensor section 35d are arranged the sameway.

One of the two strain-gage bridges, SBl, in FIG. is shown to include theaforementioned gages, it being understood that the companion bridge 5B2for a transducer associated with an adjoining half axle, or the like, isof course similar. The strain-gage grid-wires for each half of the pairconstituting the gage installation for each of the two sensor sectionsare connected in series in adjacent arms of the bridge SBl, and the twoseries-connected pairs are paralleled across the input electricalexcitation leads 43 Output from the bridge is taken across the junctionsof the respective series-connected pairs, via leads 43 Considering thepure shear condition depicted in FIG. 6, for example, the gages 39 andthe diametrically-opposite gages 40 for sensor section 350 respectivelyin compression and tension while the gages 41 and 42 for sensor section35d are respectively in tension and compression; hence the bridge isappropriately unbalanced and its output leads 43 yield a desiredelectrical output signal characterizing the vertical forces related toweight. If undesirable forces cause bending of the axle, rather thanshear-type deflection, the gages 39 and 41 would both be in compression,for example, while the other gages 40 and 42 would both be in theopposite state, tension, and the bridge would not be unbalanced, andwould develop no erroneous outputs responsive to those forces whichinduce bending; this is highly desirable, of course. Typical results ofunavoidable vertical bending forces portrayed in convenient exaggerationin FIG. 7; in that case, the two top gages experience compression andthe lower gages tension, such that there is no related output from theaforementioned bridge. Other unwanted efiects, such as those of torsionand axial elongation are simply ignored advantageously by the bridgebecause of the self-cancelling action.

In a preferred embodiment appearing in FIGS. 8 through 10, an on-boardaxle type transducer is shown as having a pair of collets 36 and 37 eachof which includes a pair of diametrically-opposite spring members 36a,36b, 37a and 3712, respectively. Collets 36 and 37 are of uniquelightweight construction which will reliably and securely secure andretain the transducer in a fixed position despite irregularities inunfinished inner surfaces of an axle, and despite extremely severeshock, vibration and temperature cycling. Each half collet, that is,each of the metal spring members 36a, 36b, 37a and 37b is independentlyadjustable, such that each collet may be independently radially expandedto lock in place the associated rigid end portion (35:: or 3512) of thesensor section without undesirably stressing that sensor section. Forsuch purposes, each spring member is fashioned in an open bowedconfiguration, which in the illustration is diamond-like and has thesides thereof joined together or formed integrally to provide aresilient doubly-bowed structure having its radially innermore cornersunited with the respective rigid end portions 35a and 35b of the sensorsection, as shown at 45a, 45b, 46a and 46b. The oppositeradially-outermore corner 47a, 47b, 48a and 48b of spring members 36a,36b, 37a and 37b are disposed and shaped to engage the inner surface ofaxle 21 over narrow line contact arcuate regions, and preferably includean outer edge coating 49, of material which is softer than the axlematerial, such that the axle surface will not be scored or scratched bythe spring members. Undesirable stress concentrations in the axle arethus minimized, while secure fitting is assured. Enlarged and relativelystiff portions about radially midway along the bowed spring members areprovided as part of the axial-com pression adjustments for the desiredradial expansions. At least two, and preferably three, angularly-spacedapertures are provided in each of the aforesaid enlarged portions of thespring members with the centrally-disposed axially-innermore aperture 51associated with each spring member being internally threaded. Anadjusting screw 52 is provided for each of the spring members, andextends through the fonward unthreaded aperture 50 into engagement withthe rearward threaded aperture 51; adjustment of the radial expanse ofthe associated spring member accompanies axial compression of thedoubly-bowed spring member, as the screw is tightened. As is shown inFIGS. 9 and 10, the adjusting screws 52 are all adjusted from theout-board end of the axle 21, whence the transducer is accessible. Tomake the adjusting screws 52 associated with the inner collet 36 readilyadjustable from the outer end of the axle, an otherwise-unused aperture54 is provided in each of the spring members 37a and 37b, and, further,collet member 36 is angularly offset somewhat in relation to colletmember 37 to align adjusting screws 52 associated with collet member 36with the access-apertures 54 in collet member 37. Adjusting screws 52associated with collet member 36 are readily accessible from the outsideof the axle by way of a tool inserted through the apertures 54 and intoturn-inducing engagement with the appropriately-shaped heads of thescrews 52. Each of the spring members 36a, 36b, 37a and 37b is alsoshown to be provided with apertures 55 which serve the purpose ofimparting symmetry to the spring members which promotes even loading andavoids undesirable stress concentrations.

When the screws 52 are loose and the spring members 36a, 36b, 37a and37b are unexpanded, the transducer assembly with which they areassociated may be slid into the axle from the out-board end thereof to adesired axial position. Once in the proper position, the individualspring members may be radially extended by tightening the individualadjusting screws 52 to a predetermined torque by long-handled toolingsuch that the spring members will make narrow-area contact with the axleand bind the transducer so tightly in place as to preclude significantdisplacement. The spring members are capable of storing sufficientenergy to compensate for such dimensional variations in the interior ofthe axle as will be caused by environmental conditions. Undesirablebending of the relatively delicate sensor section tends to developduring the mechanical mounting of the transducer within the axle, due tothe need for mounting it at axially-spaced positions, and because ofpossible inaccuracies in the fabrication of the transducer and/orirregularities in the shape and surface characteristics of the axle.Because the spaced collets are formed by individually-adjustable springmembers, the aforementioned undersirable bending can be eliminatedreadily and the sensor section can be secured in place substantiallystress-free. By observing the outputs of the bridge circuitry associatedwith the sensor section gaging, using convention instrumentation,undesirable bending effects are immediately detected, and selected onesof the screws 52 are then adjusted, while making such observations untilthe unwanted bending effects are cancelled; this affords a highlyadvantageous and convenient means for obtaining a zero balance withrespect to bending characteristics. The same kind of practice alsoenables any desired pre-loading effects, or the like, to be introduced,very simply and accurately. By way of distinction, prior fasteningmechanisms have involved circumferential locking by way of simultaneousexpansions essentially all around a sensor axis, such that the axisitself could not be shifted radially; the individual radial adjustmentsprovided on opposite sides of a sensor axis, by way of the presentteachings, instead permit each end of the generally-centralized sensorsection to be centered or shifted, as necessary, without affecting theintegrity of the structure or the setting at the opposite end.

The illustrated preferred sensor section includes a pair ofaxially-spaced, thin-walled and relatively flexible shear-sensingportions, 350 and 35d, spaced by an enlarged and relatively rigidaxially-extending mid portion :44, and joined at their axial extremitieswith rigid end portions 35a and 35b. The lengths of the relativelyflexible shearsensing portions 35c and 35d are shown to be suflicient toaccommodate the internal gaging 39 and 40, and to accommodate certaindeflection-induced elastic deformations. In FIG. 9, the locus of gagingis shown to be close to the rigid end portions 35a and 35b, whereoptimum measured elastic deformation effects are experienced. A hollowcylindrical shear-sensing section is preferred, and conveniently andeconomically lends itself to precision manufacture, although it shouldbe appreciated that the cross-section may be other than of perfectlycircular tubular form. Conveniently, the internal strain gaging of thesensor unit may be hermetically sealed by a cover plate for electricalconnection leads, and an end housing 53 filled with potting compound(not shown) accommodates a cable connector and other desirable auxiliaryitems.

Axle thickness may not always be uniform and may, in fact, be of anon-uniform cross-section such as that of the tapering constructionshown in FIG. 9, resulting in normally troublesome non-uniformdeflection characteristics for the axle. The same may also be true wherean axle is of uniform thickness along the specific region occupied bythe transducer but is surrounded or otherwise influenced by otherportions of different cross-section or by other members, such asbearings, beam joints and the like. For such reasons, and as shown inFIG. 9, rigid end portions 35a is caused to extend a greater axialdistance than rigid end portion 35b, whereby sensing sections 350 and35d are asymmetrically disposed with respect to the transverse planes ofsupport defined by the outer edges of the collet members. Suchasymmetrical disposition of the sensing sections functions to.compensate for the asymmetrical deflection of the non-uniform thicknessaxle 21. In this connection, references to FIGS. 6 and 7 serves to aidin understanding the behavior of the axle and sensor unit; where onepart of an axle is thinner, it will bend more under loading, and theflexible sensor sections within thus will not bend in the same uniformway they would if the axle cross-section were uniform throughout. Thepresence of shear-responsive gages at two axiallydisplaced sites, i.e.at the two sensor sections 350 and 35d in the structure underdiscussion, is primarily for the purpose of enabling their unwantedbending responses to cancel one another in their bridge-circuitarrangement, yet such cancellation will not occur, and error willresult, if they respond unequally to unequal bending because of thenon-uniformity of the axle. Accordingly, the responses of these sensorsections to bending is intentionally caused to be different, bypredetermined amounts, by the aforesaid asymmetrical dispositions ofthese sections. As shown in FIG. 9, the sensor section which is nearerthe thicker cross-section, i.e., section 35c, is moved further from theplane of its collet support, to cause the wanted offsetting increase inits bending, so that its bending will then substantially match that ofthe other section 35d, and their respective unwanted gage outputs due tobending effects will cancel while their wanted outputs due tosubstantially pure shear will augment one another. It is not essentialthat the mid portion 44 be rigid for the aforementioned beneficialeffects to take place, but the mid portion 44 has the advantageousaction of effectively multiplying the consequences of axle deflections,whereby more pronounced responses are developed by the strain gages thanwould be the case if the tubular unit were of the same flexibilitythroughout the length between the rigid end portions 35a and 35b. Therigid mid portion 44 may be disposed asymmetrically in relation to therigid end portions 35a and 35b, for purposes of causing the two sensingportions 35c and 35d to be of different lengths, and, in turn, todevelop intentionally different responses for introducing certaincompensations, such as those for non-uniform axle cross-sectionsreferred to hereinabove. Similarly, like asymmetrical effects may bedeveloped, or unintended asymmetrical effects may be overcome, bymachining down selected parts of the mid portion to impart a desireddegree of flexibility at a site such as that of the annular groove 44ain FIG. 9. Comparable effects may be realized by precision machiningoutside of the appropriate one of the sensing portions to a diameterless than that of the other.

The transducer 34 including the sensor unit and associated colletmembers is illustrated as a unitary member with no relatively movingparts which would tend to create troublesome hysteresis or frictionaleffects causing errors which would be sensed by the gages and displayedin the measurements. However, where it is not possible to install aunitary transducer within an axle, because of unusual internalconfigurations in axle construction, for example, it may then bewarranted to construct the transducer of several parts for assemblywithin the axle.

The collet arrangement shown in FIG. 11 includes spring members 56a and56b which are attached to the rigid end portion 63 of the sensor unit bymeans of cooperating tapered surfaces and a locking member 64. It is tobe noted that the spring members 56a and 56b may be formed integrallywith the rigid end portion of the sensor unit as in the aforementionedembodiment. A pair of ring members 57 and 58 are concentric with thesensor unit and are interconnected with spring members 56a and 56b bymeans of sections 59 and 60' which are formed integrally therewith. Anadjusting screw 61 extends through and is threadedly engaged with anaperture in ring member 58 and is threadedly engaged at the other endthereof with an adjusting nut 62 such that by tightening the adjustingscrew 61, the spring member 56a is radially extended and by looseningthe adjusting screw 61, the spring member 56a is brought radiallyinward.

A typical installation is represented in FIG. 18, wherein an aircraftnose wheel unit 78 and right and left main wheel units 79 and 80 areeach equipped with the improved transducers within the axles near eachWheel at sites marked X. Cabling 78a-80a couples the transducermeasurement information through the struts 78b- 80b to an on-boardinstrumentation package 81. The latter provides visual gross weight andcenter-of-gravity displays 81a and 81b in accordance with knowntechniques; total weight is determined by adding the weights detected atthe sites of each of the wheels, and centerof-gravity is computed byconsidering the moments of the wheel reactions (longitudinal and/orlateral) in relation to reference positions. Landing and lift-offconditions may be established from the weight signals also, although theconventional measurements are made while the craft is stationary.

The specific embodiments and practices herein described have beenpresented by way of disclosure rather than limitation, and variousmodifications, substitutions and combinations may be effected by thoseskilled in the art without departure in spirit of scope from thisinvention in its broader aspects and as set forth in the appendedclaims.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. Transducer apparatus comprising a load sensor unit having surfaceswhich exhibit strain responsive to loadings thereof, collet means forfixedly mating said sensor unit radially and axially in relation to acooperating loadsupporting member to exhibit strain response to loadingswhereby, said collect means including at least two radially-expansibleportions arrayed in substantially the same plane at different angularpositions to support said sensor unit radially about a center and inrelation to said load-supporting member, each of saidradially-expansible portions including members which cooperate toproduce a toggle-like radial expansion in response to lateral pressure,and means independently adjustable to apply lateral pressure to saidmembers of each of said portions, and gage means for producingelectrical output signals characterizing strain responses of said sensorunit to loadings thereof transferred to such unit by said collet means,

2. Transducer apparatus as set forth in claim 1 including at least twoof said collet means mounting said sensor unit at spaced positionstherealong, each of said portions of each of said collet means havingnarrow peripheral edge surfaces which form a substantially line contactwith at least one of the adjoining peripheral surfaces of theload-supporting member and the load sensor unit.

3. Transducer apparatus as set forth in claim 1 wherein said memberswhich cooperate to produce a togglelike radial expansion are springmembers, and wherein each of said portions of said collet meanscomprises two of said spring members which are of bowed form.

4. Transducer apparatus as set forth in claim 3 wherein said two springmembers of bowed form are arranged back-to-back with their radiallyouter and inner edges together and other portions spaced further apart.

5. Transducer apparatus as set forth in claim 3 wherein the two springmembers of each of said collet portions are back-to-back with agenerally diamond-shaped spacing therebetween and have a first corneredge thereof affixed to said sensor unit and a second opposite corneredge thereof radially displaced from said sensor unit and adapted toengage said load-supporting member.

6. Transducer apparatus as set forth in claim 5 wherein third and fourthcorner edges of the arrangement of said spring members have alignedapertures therein with surfaces surrounding at least one of saidapertures being threaded, and wherein said independently adjustablemeans includes a threaded bolt member extending through said aperturesand threadedly engaged with said surfaces.

7. Transducer apparatus as set forth in claim 6 wherein said third andfourth corner edges are substantially rigid.

8. Transducer apparatus comprising a load sensor having substantiallyrigid end portions and at least one relatively deformable portionbetween and joined as a unit with said end portions, collet means formounting said end portions in relation to a load-supporting member atspaced positions therealong, at least one of said collet means includingat least a pair of spring means arrayed in substantially the same planeand each individually radially expansible and each having narrowperipheral edge surfaces which form a substantially line contact insubstantially the same plane with at least one of the peripheralsurfaces of the load-supporting member and of the sensor end portionbetween which it is disposed, said spring means of each of said colletmeans being angularly displaced at different angular positions aboutsaid sensor to support said sensor radially in relation to saidload-supporting member, and gage means for producing electrical outputsignals characterizing deformations exhibited by the load-supportingmember and transferred to said deformable portions of said load sensorvia the line contact of said edge surfaces of said collet means.

9. Transducer apparatus as set forth in claim 8 wherein each of saidspring means includes members which cooperate to produce toggle-likeradial expansion in response to lateral pressure, and meansindependently adjustable to apply lateral pressure to said members ofeach of said spring means, whereby said spring means provide secureconnections with said load-supporting member while remaining yieldableradially to compensate for dimensional changes in said load-supportingmember due to environmental effects.

10. Transducer apparatus as set forth in claim 9 wherein each of thespring means includes two of said members in a back-to-back arrangementwith a generally diamond-shaped spacing therebetween and having a firstcorner thereof aflixed to said rigid end portion and a second oppositecorner thereof radially displaced from said rigid end portion andadapted to engage said load supporting member, and wherein third andfourth comers of said arrangement have aligned apertures, surfacesbordering at least one of said apertures being threaded, and whereinsaid means for applying lateral pressure and thereby adjusting therelative positions of said first and second corners including a threadedfastening member extending through said apertures and threadedly engagedwith said surfaces.

11. Transducer apparatus as set forth in claim 10 including two of saidcollet means, one each at each of said spaced positions, alignedapertures through said third and fourth corners of one of said colletmeans being further aligned with aligned apertures of the other of saidcollet means and thereby affording access for adjustment of saidadjusting means for said other collet means.

12. Transducer apparatus as set forth in claim 8 wherein said relativelydeformable portion of said load sensor includes substantially tubularelastically-deformable material of substantially annular cross-sectionbetween and joined as a unit with said rigid end portions and exhibitingsurface strains responsive to loadings thereof, said loadsupportingmember being hollow, and said collet means being disposed within saidload-supporting member and applying loading forces to said end portionsof said load sensor in directions substantially normal to thelongitudinal axis of said tubular material, one of said rigid endportions being joined with said tubular material at a greater distancefrom the plane of line contact for the associated collet means thereforthan is the other of said end portions, whereby said tubular material isasymmetrically disposed longitudinally with respect to the planes ofsaid line contact of said collet means, said electrical strain gagemeans including at least one pair of electrical strain gages bondedrespectively to diametrically-opposite surfaces of said tubular materialat each of two positions axially spaced along said longitudinal axis.

13. Transducer apparatus as set forth in claim 8 wherein each of saidcollet means consists of two of said radiallyexpansible spring meanssubstantially diametrically opposed to one another.

14. Transducer apparatus as set forth in claim 12 wherein said tubularmaterial between said rigid end portions comprises two axially-spacedrelatively-deformable sections joined with a relatively rigidmid-section axially therebetween, said pairs of strain gages each beingdisposed at a different one of said two spaced sections and respondingto load-induced strains thereof.

15. Transducer apparatus as set forth in claim 12 wherein saidload-supporting member comprises a vehicle axle, and wherein said straingages at each of said positions are disposed along vertically-oppositesurfaces.

16. Transducer apparatus as set forth in claim 15 wherein each of saidstrain gages includes electrically-conductive filaments extendingsubstantially longitudinally along said surfaces of said tubularmaterial, for response to shearinduced elastic deformations of saidmaterial.

17. Transducer apparatus as set forth in claim 12 wherein said gagemeans includes electrical bridge circuitry having electrical excitationterminals and electrical output terminals, and means connecting saidstrain gages in said circuitry as arms thereof to unbalance saidcircuitry in response to deformations of said material induced by shearof said load-supporting member while preserving said circuitrysubstantially balanced in response to deformations of said materialinduced by bending of said load-supporting member.

18. Transducer apparatus as set forth in claim 12 wherein saidload-supporting member is more rigid nearer one of the said planes ofcontact and tends to bend non-uniformly, said one of said end portionsbeing further from said one of said planes and thereby being effectiveto induce correspondingly greater relative bending of the nearby tubularmaterial in response to bending of said loadsupporting member.

19. Transducer apparatus comprising a load sensing device includingsubstantially rigid end portions and substantially tubularelastically-deformable material between and joined as a unit with saidend portions and exhibiting surface strains responsive to loadingsthereof, means for applying load forces to said end portions of saidload sensing device in directions substantially normal to thelongitudinal axis of said tubular material, first strain gages bonded tosaid tubular material nearer one of said end portions and responding toload-induced surface strains thereof, substantially parallel with saidaxis second strain gages bonded to said tubular material nearer theother of said end portions and responding to load-induced surfacestrains thereof, substantially parallel with said axis said tubularmaterial nearer said one of said end portions and said tubular materialnearer said other of said end portions being united with andlongitudially spaced along said axis by a substantially rigid elongatedmid portion, electrical bridge circuitry having electrical excitationterminals and electrical output terminals, and means connecting saidstrain gages in said circuitry as arms thereof to unbalance saidcircuitry in response to deformations of said material induced bydisplacements of said end portions in shear while preserving saidcircuitry substantially balanced in response to deformations of saidmaterial induced by displacements of said end portions in bending.

References Cited UNITED STATES PATENTS 3,272,006 9/1966 Eckard 73141 A3,327,270 6/1967 Garrison 3382 3,426,586 2/1969 Kadlec 73--88.53,494,181 2/1970 Boelkins 73-88.5 3,521,484 7/1970 Dybvad et a1. 7388.5

RICHARD C. QUEISSER, Primary 'Examiner J. WHALEN, Assistant Examiner US.Cl. X.R. 73141 A,

